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Laser printer draws current in a spike, what for?

Discussion in 'Electronic Basics' started by ~Dude17~, Aug 29, 2004.

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  1. ~Dude17~

    ~Dude17~ Guest

    X-No-Archive: Yes

    I've got a laser printer that draws current in spikes and it
    makes the lights flicker as well as causing a UPS on the same circuit
    to switch over to battery due to excessive dV/dT. Unfortunately, I
    don't have a way of putting the printer on its own circuit unless I
    want to use a long extension cord.

    When it's in sleep state, it draws about 0.22A. When I print
    something, it draws about 8A RMS to heat up. After it's done
    printing, it stays in "ready to print" state for about ten minutes
    before going to sleep and this is where problem starts.

    Had the printer for a while, but I finally bothered to check it out on

    I captured the event on my storage oscilloscope and this is what I

    At the start of cycle it draws 26A RMS for about 32mS or two cycles
    and tapers down to 8.5A RMS after 550mS. Between the start and 550mS,
    there's two spikes of about 8mS where current is only drawn from half
    of the cycle. After 550mS, the current draw drops to 0.22A RMS, then
    starts this whole cycle again after 15 seconds.

    If you're a visual type of person, here's the actual capture:

    Is there a reason it needs to draw current in this pattern instead of
    spreading it out over a longer period of time?
  2. Anthony

    Anthony Guest

    (~Dude17~) wrote in

    I suspect it may be the heating coils.


    You can't 'idiot proof' anything....every time you try, they just make
    better idiots.

    Remove sp to reply via email
  3. artie

    artie Guest


    heater for the fuser assembly. On the first couple of generations of
    laser printers, they didn't even bother to use a zero-crossing switch,
    and that really made the lights flicker!
  4. Rich Webb

    Rich Webb Guest

    it's the heating element for the fuser, maybe a halogen lamp element
    inside the fuser cylinder. You're seeing a resistive current draw from
    the 60 Hz mains that tapers off as the element heats up and increases
    resistance. Your 26 amp initial draw is reasonable for a cold
    (relatively) element resistance of around 5 ohms.

    The steady state value it's approaching is around 8 A, as you've
    described, as it reaches operating temperature. There's probably a
    bang-bang thermostat that pokes the heater when it has gotten too cold
    and runs the element until it reaches the other setpoint.

    Absent reprogramming the temperature controls (probably do-able, esp if
    you could dig up the tech manual) the best bet is just to turn it off
    when not in use.

    WRT the "drop out" cycles every 200 msec or so. Guessing but *maybe*
    they measure the temperature as a function of element resistance (saves
    the cost of a separate sensor) and are not triggering the heater during
    those half-cycles in order to measure the filament resistance (with an
    RC to a comparator and a timer?).
  5. Ian Stirling

    Ian Stirling Guest

    One 'easy' way might be to find an appropriate NTC thermistor, and put
    it in series with the lamp.

    Maybe several small ones for their lower thermal mass.
  6. Let me guess... it's a LaserJet 4 or 5. It's keeping itself warmed up,
    using heating coils.

    We have moved to newer printers because the old ones were drawing so much
    current they would disturb computers on the same circuit.
  7. Spajky

    Spajky Guest

    would blow it; mine halogen lamp element inside the fuser cylinder has
    400W ...

  8. I have a Brother HL-1470N, at home, which exhibits the same symptoms.

    I too was thinking of posting about this. I am trying to figure out
    what to do about this. In my case, I simply moved it off of the UPS,
    but the lights flickering is still undesirable.

    Is there anything I can actually do about this?
  9. I read in that Anthony Guzzi
    You definitely did the right thing in moving it off the UPS. There is no
    justification, normally, for running a printer off a UPS, and, as you
    see, it is a very stressful load which could adversely affect the UPS
    life or reliability.

    A laser printer sold in Europe must conform to EN 61000-3-2 and -3. The
    former is concerned (indirectly) with limiting the peak pulse current,
    cycle by cycle, while the latter is concerned with limiting flicker. But
    you'd need to run it from 240 V - either directly or with 120:240
    transformer. The frequency doesn't matter.

    According to US sources, problems such as you report never occur, and
    they don't need to implement the IEC versions of those ENs as US
    standards. So you are actually just imagining the flicker. (;-)
  10. John G

    John G Guest

    Might be interesting if you told us what Brand/model printer you are
    complaining about.

    Was a know fact in early laser printers.
  11. Bob Masta

    Bob Masta Guest

    I've got a Brother HL-1440 that also causes me to imagine the
    lights are flickering. ;-)

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  12. Dave Holford

    Dave Holford Guest

    My NEC Superscript 860 has the same effect on my imagination!

  13. Dave VanHorn

    Dave VanHorn Guest

    What you're seeing, is the cycling of the heater for the fusing roller.
    This roller melts the toner into the paper.
    Without it, your print would simply blow away.
    It's integral to the operation of the printer.. Just don't put it behind
    your ups. There's really no need anyway, if the power goes out, then just
    restart the print later.
  14. The irony is this is quite common in the US, but I've never seen
    it happening in a 240V country ;-)
  15. Guest

    | In article <>,
    |> According to US sources, problems such as you report never occur, and
    |> they don't need to implement the IEC versions of those ENs as US
    |> standards. So you are actually just imagining the flicker. (;-)
    | The irony is this is quite common in the US, but I've never seen
    | it happening in a 240V country ;-)

    We do have 240 volts. The problem is that we also have the NFPA that
    publishes the NEC which in 210.6(A)(2) restricts the voltage for cord
    and plug equipment to a maximum of 120 volts relative to ground, thus
    disallowing the use of the 240 volt connection for the typical laser
    printer. Of course one might get around this if they say it is a 26A
    load instead of a 8A (relative to 120 volts).

    I guess I should put this in the "favorite beef with the NEC" thread.

    I don't know that this would affect it all that much, but I've also
    heard that in UK, available fault current at homes tends to be higher
    than in the US (one transformer serving a whole block of homes instead
    of the typical 1 to 4 in the US). I'm not sure I'd really like having
    higher available fault current.
  16. Well... obviously the current is halved, but...

    A laser printer that dims the lights???? Jus how common is
    that, really?
  17. I've seen it (NEC Silentwriter LC890). It's just a flicker- the
    problem is that the flicker is repetitive with the control of the
    fusion roller temperature and continued as long as the printer was
    switched on. My modern HP doesn't appear to do anything like that.

    Best regards,
    Spehro Pefhany
  18. ~Dude17~

    ~Dude17~ Guest

    X-No-Archive: Yes


    me three. Mine's a BROTHER too. Brother DCP-1200 Scanner/Printer
    combo and it's not that old. Perhaps Brother's got an issue with
    their heater drive algorithm. It's ok if it's held on and caused a
    flicker every once in a while.

    To the people who pointed out it's the heating element, I'm aware what
    the power is used for. My question was what the logical reason is for
    pulling current in the pattern my printer does.

    I don't plug my laser printer into my UPS and only stupid users plugs
    one into an under the desk sized UPS. What I'm saying is Irise(dI/dT)
    is extremely fast. This in turn causes a line drop at high dV/dT. My
    UPS, which is on the same branch circuit transfers to battery every
    time the printer pulls a surge current.

    UPS circuit transfers to battery in prediction of upcoming serious
    power problem not because the voltage drops too much, but rate of
    change of voltage (dV/dT) is excessive. When the cause of transfer
    information is extracted from UPS, it reports as "R", which means
    unacceptable rate of voltage change on APC UPS.

    What did I do? I put the UPS on a different branch circuit with an
    extension cable and changed the ballast in light fixture to one
    equipped with an active PFC.

    You might ask why active PFC ballast. The power factor controller IC
    is actively monitoring AC phase and DC bus voltage and it creates a
    near unity power factor as well as maintain a steady voltage on the DC
    bus. The controller samples the AC many times a cycle(In hundreds of
    KHz range) which is a must to correct power factor. The controller
    compensates for voltage dip and drives the MOSFET accordingly to
    maintain a steady DC bus voltage. Steady DC bus ensures flicker free
    lamp operation.

    For us home users, "just put the printer on a dedicated circuit" isn't
    really an option.
  19. Ian Stirling

    Ian Stirling Guest

    I wonder how often 4 or 5 printers on one circuit might cause the
    fuse to pop, if "idle".
  20. I read in that wrote
    The transformer impedance is lower but the cables add impedance (mostly
    inductance unless they are buried coaxials). The typical fault currents
    in UK and US are not a lot different, i.e. in USA the impedance of a 120
    V supply is about half that of a European 230 V supply. But note
    'typical'. There is a lot of variation.
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